We present the first search for the pair production of dark particles X via
KL0ββXX with X decaying into two photons using the data collected by
the KOTO experiment. No signal was observed in the mass range of 40 -
110~MeV/c2 and 210 - 240 MeV/c2. This sets upper limits on the branching
fractions as B(KL0ββXX)< (1-4) Γ 10β7 and
B(KL0ββXX)< (1-2) Γ 10β6 at the 90% confidence
level for the two mass regions, respectively